Study on PoP reliability with different edge bonding during thermal cycling by finite element methods

In order to improve the thermal fatigue lifetime of Package-on-Package (PoP), this paper taking PoP thermal reliability the cost and rework into consideration, different edge bonding structure (i.e. 100% edge bonding, 50% edge bonding, and 10% edge bonding) are used to improve thermal reliability. At the same time, the effect of different edge bonding patterns (i.e. only the bottom packege, or both the top and the bottom packeges) on the reliability is evaluated. We present that both edges bonding structure and edge bonding pattern have an effect on PoP thermal reliability by finite element analysis (FEA) under thermal cycling. After the analysis of the stress and the strain distribution, it was found that the outmost solder joint on bottom package was the most dangerous positon. Thermal fatigue lifetime of PoP with different edge bonding is analyzed based on plastic strain model by FEA. The study results reveal that edge bonding seems to have better contribution to PoP thermal reliability than underfilling, and the thermal fatigue lifetime of only bottom package edge bonded is longer than both the top and the bottom packages edge bonded, owing to the solder joints are overcommitted and the CTE of edge bonding epoxy is higher than substrate, PCB and solder joints. In addition, the thermal fatigue lifetime of 10% edge bonding is longest than others.